I once read some advice from a random person on the internet that concerns me.

Shocking, I know.

In researching credit scores, I found this advice from esteemed credit expert “Anonymous” about sites that offer your free credit score:

“[Sites like] Credit Karma show your fake TransUnion and Equifax scores, using the Vantage 3.0 system instead of the FICO system… I warn highly against using these free services because in my case, my credit scores… were inflated and inaccurate.”

OK, Anonymous. You’ve got my attention.

What is a “fake” credit score, and are the free scores I’m seeing online way off from what’s used to determine whether I get a loan or credit card?

Short answer: No, the score you see isn’t “fake,” and no, it’s not “inflated.” But, yes, it is probably different from what your bank and others see when they run a credit check.

You can get a free credit score and credit report from a site like Credit Sesame to get an idea of where you’ll stand with lenders. But it’s not exactly what they see.

Let’s find out why.

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The Difference Between Credit Scores

We have three major credit-reporting agencies: TransUnion, Equifax and Experian. They keep track of your financial activity and produce reports that list your credit history.

To create your credit score, these agencies — and a bunch of smaller ones that do a similar job — each use a complicated formula to turn your credit activity into a sort of grade.

The reason there’s a difference between credit scores is partly because two models for computing your score dominate the market: FICO and VantageScore.

Both models have the same goal: to determine whether you’ll be able to repay a loan in a timely manner. They use the same information — credit reports from the three major agencies — but weigh various factors differently.

It’s like how you could always get an A on a paper in Ms. Jones’ class, but got a C from Mr. Johnson. The latter cared about word count, while Jones only graded on the quality of your writing. #TeamJones

To put it another way, Carla Blair-Gamblian, a consultant team lead at Veterans United Home Loans, told me, “A good comparison would be Celsius versus Fahrenheit. A 700 on one scale isn’t the same as a 700 on the other.”

That’s true, though the scales have become more similar in recent years. When VantageScore first came along in 2006, its scale ran from 501 to 990. But VantageScore 3.0, launched in 2013 — and the updated VantageScore 4.0, launched in 2017 — mirrors FICO’s scale of 300 to 850.

On top of these popular models, some smaller agencies might use their own models to determine your credit score.If your bank or credit card company uses one of these agencies for your credit check, it’ll see a credit score you’ve probably never seen before.

How Do You Know When You’re Looking at the Right Credit Score?

So, you want to stay on top of your credit score. You don’t want to apply for a loan or credit card with no idea how you’ll fare — that’s an unnecessary ding on your credit report.

But how do you know you’re even looking at the right information?

The bad news: You might not ever see the exact score your creditor sees when they run a credit check.

Good news: You can still arm yourself with the best information available.